The present invention relates to check valves for use with vehicle fuel tanks and, more particularly, to check valves having a valve body for mounting in a flow path, formed in a casing body, which opens and closes the flow path according to the difference between pressures applied to both sides of the valve body.
In order to protect a fuel tank from the variations in vapor pressure therein, a check valve of this type is built in a two-way valve which is provided between the fuel tank and a canister (cf. Unexamined Japanese Patent Publication (Kokai) Sho-60-184779/(1985)). The check conventional valve will be described with reference to FIG. 9.
In FIG. 9, reference numeral 200 designates such a conventional two-way valve. The two-way valve 200 has a partition wall 206 which divides the space in a casing body 202 into upper and lower valve chambers 203 and 204. The upper valve chamber 203 incorporates a check valve 210 and is sealingly closed with a cover 212, while the lower valve chamber 204 incorporates a diaphragm valve 220, and it is also sealingly closed with a cover 222.
As the internal pressure of the fuel tank increases, the pressure in a tank-side connection port TP is increased. When the pressure in the tank-side connection port TP becomes a predetermined pressure higher than atmospheric pressure, it is applied to the valve body 224 of the diaphragm valve 220 through a passageway (not shown), so that the valve body 224 is moved away from its seat 228 against the elastic force of a spring 226, to allow the fuel vapor in the fuel tank to move into the canister.
When, on the other hand, the internal pressure of the fuel tank decreases, and the difference between the pressure in the tank-side connection port TP and a canister connection port CP becomes higher than a predetermined value, the valve body 214 of the check valve 210 is moved away from its valve seat 218 against the elastic force of a spring 216 mounted on a spring receiving member 217; that is, the check valve 210 is opened to return the fuel vapor from the canister into the fuel tank. As was described above, the valve body 214 of the check valve 210 is supported through the spring receiving member 217 by the spring 216. Hence, the check valve 210 is opened by the elastic force of the spring and the difference between the pressure in the canister connection port CP and the pressure in the tank-side connection portion TP. The valve body 214 of the check valve 210, as shown in FIG. 9, has a thin portion and a thick portion which are coaxial with each other.
The above-described conventional check valve suffers from the following problem: When the pressure difference is in an ordinary range (for instance, from 200 mm Aq to 300 mm Aq), the valve body 214 is vibrated slightly by resonance, thus producing noise. In addition, the intrinsic oscillation characteristic of the valve body 214 and the above-described slight vibration cause a resonance phenomenon in combination, thus amplifying the noise.
A solution to this problem is known. That is, the diameter of a hose (not shown) connected to the canister connection port CP is increased, or the length of the hose is changed, to shift the range of flow rates with which the resonance takes place. However, increasing the diameter or length of the hose not only increases the manufacturing cost of the valve but also obstructs the miniaturization of the latter.